Tube sheet welding with inert gas pressure at the joint

ABSTRACT

A method and apparatus is disclosed to horizontally butt fusion weld a tube to a tube sheet. A chill bar surrounds the butted joint forming a chamber around the joint to contain an inert gas under pressure. An orbital type welder is inserted inside the tube adjacent the butted joint and the interior atmosphere surrounding the electrode is pressurized with a second inert gas at a pressure higher than the inert gas in the chamber surrounding the exterior of the butted joint to prevent the weld puddle from falling by gravity into the inside of the horizontally disposed tube and tube sheet during the welding operation.

Roberts et al.

TUBE SHEET WELDING WITH INERT GAS PRESSURE AT THE JOINT Inventors: JohnG. Roberts, Thousand Oaks;

Jack Weber, San Jose; Secondino P. Margherio, Van Nuys, all of Calif.

North American Rockwell Corporation, El Segundo, Calif.

Mar. 20, 1972 Assignee:

Filed:

Appl. No.: 236,300

US. Cl. 219/125 R, 219/60 A, 219/74,

Int. Cl 823k 9/12 Field of Search 219/60 A, 60 R, 61, 219/124, 125 R,l26, 137, 74, 160, 72, 8.5

References Cited UNITED STATES PATENTS ]Aug. 21, 1973 1,872,114 8/193211111111111 ..2l9/61X 2,716,692 11/1955 w111i111111=1111..... 2,716,6918/1955 Bowman 3,018,358 l/l962 Schaaf, 11. ..219/72 Primary Examiner-J.V. Truhe Assistant Examiner-L. A. Schutzman Attorney-L. Lee Humphries.Henry Kolin et al.

[5 7] ABSTRACT A method and apparatus is disclosed to horizontally buttfusion weld a tube to a tube sheet. A chill bar surrounds the buttedjoint forming a chamber around the joint to contain an inert gas underpressure. An orbital type welder is inserted inside the tube adjacentthe butted joint and the interior atmosphere surrounding the electrodeis pressurized with a second inert gas at a pressure higher than theinert gas in the chamber surrounding the exterior of the butted joint toprevent the weld puddle from falling by gravity into the inside of thehorizontally disposed tube and tube sheet during the welding operation.

7 Claims, 6 Drawing Figures Patented Aug. 21, 1973 2 Sheets-Sheet 2 FIG.2

FIG. 3

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TUBE SHEET WELDING WITH INERT GAS PRESSURE AT THE JOINT BACKGROUND OFTHE INVENTION 1. Field of the Invention Prior art methods to join tubesto tube sheets include the following. Most heat exchangers, conventionalfossil fuel systems, and the like, join thin tubes to headers or tubesheets by inserting the ends of the tubes into apertures in the headeror tube sheet until the ends of the tube are flush with the outer faceof the header, followed by welding of the end of the tube adjacent theface of the header. An alternative method includes pressing the ends ofthe tube into a recessed housing, followed by fusion welding of thetubes in place exteriorly of the tubes.

In the field of nuclear reactors it is extremely important forsuccessful operation of the reactor to achieve an absolute leaktightness of all the tubes and tube sheet joints. The foregoing priorart practices just described do not achieve a complete fusion of thetube to the tube sheet since they are welded exteriorly of the tubes. Amethod for joining tubes to a tube sheet which includes a butt fusionweld process is shown in an article in the Welding Journal, July 1960,pages 2-6, by Messrs. Rowlands and Cooksey. The butt fusion weld isaccomplished from the inside of the tube, thus a complete fusion of theends of the tube to the adjacent tube sheet stub is provided since theweld goes completely through both the tube and tube sheet stub,providing an effective joint. FIG. ll) of the article shows that thebutt fusion weld is completed when the tube and tube sheet stub areoriented in a vertical direction. Gravity does not cause the molten weldpuddle to drop into the interior of the tube during the fusion weldprocess since the orientation of the tube is in the vertical direction.However, a problem peculiar to the nuclear art arises in that the heatexchangers are lengthy, thus it becomes advantageous and practical tofabricate the heat exchangers in a substantially horizontal position.Thus, it can be seen that to fusion weld the tubes in the heatexchangers to tube sheet stubs or headers, the weld puddle formed by thewelding sequence tends to fall out by gravity, thus complicating thesensitive weld sequence.

SUMMARY OF THE INVENTION It is an object of this invention to provide amethod to fusion butt weld tubes to a tube sheet on a horizontal plane.

More specifically, itis an object of this invention to fusion butt weldtubes to tube sheet stubs in a horizontal plane by providing a methodand apparatus for backing the molten weld puddle during the fusion weldcycle.

The method devised includes the following. The basic components includea split assembly or chill bar fabricated from a material of, forexample, copper, with clamping screws for retaining the chill bar forassembly on the workpiece, namely, the tube to the tube sheet stub orheader. The copper chill bar assembly has a gas manifold with outlets topurge the outside of the workpiece and the weld nugget with an inert gasduring the welding cycle. A groove in the copper chill bar providesspace for the inert gas coverage and backup casting or die for themolten weld nugget. An internal plug with a measured orifice therein isinserted downstream of the weld joint to provide an internal gaspressure seal, thus providing a chamber for an inert atmospheresurrounding the welding head. An orbital type welder is insertedinteriorly of the header and tube and has its welding tip or electrodedirected radially outwardly adjacent the joint of the tube and the tubesheet. A source 5 of inert gas under pressure is admitted through theorbital welder apparatus to the interior of the tube and tube sheet stubor header. The inert gas under pressure is supplied to the chambersurrounding the electrode or the orbital welder during the weldingoperation to provide a backup pressure for the molten weld puddle,thereby forcing the molten puddle into the backup groove or die of thecopper chill bar surrounding the butted joint. Thus, it can be seen thatsagging of the molten weld puddle in response to gravity is preventedand welding with the workpiece or tubes in a substantially horizontalposition may be accomplished satisfactorily. The small orifice in theinternal plug is provided so that as the internal inert gas underpressure enters the chamber surrounding the orbital welding electrode,it forces any gas impurities such as oxygen through the measured orificeso that a completely inert atmosphere may be provided. The interiorinert gas is under higher pressure than the gas within the chamber,formed bythe chill bar surrounding theexterior of the butted joint sothat the puddle is forced into the chill bar groove.

Therefore, an advantage over the prior art is the method in which themolten weld puddle is prevented from falling out of the joint formed bythe tube and tube sheet during a sutstantially horizontal fusion weldprocess. I

BRIEF DESCRIPTION. OF THE DRAWINGS The above noted objects andadvantages of the present invention will be more fully understood upon astudy of the following detailed description in conjunction with thedetailed drawings in which:

FIG. 1 is a partially cutaway plane view of the preferred embodiment ofthe invention illustrating a butted tube joined to a tube sheet stubwith a chill bar positioned around the butted joint having an orbitalwelder inserted interiorly of the tube adjacent the butted joint toperform the welding operation;

FIG. 2 is an enlarged view of the chill bar assembly surrounding thetube and tube sheet stub joint, illustrating the various apertures forinjecting theinert gas both exteriorly and interiorly of the weld joint;

FIG. 3 is a view taken through lines 3-3 of FIG. 2, illustrating theclamping method utilized to join the top and bottom segments of thechill bar;

FIG. 4 is a planeview of the device used to insert the interior plugwithin the tube downstream of the weld joint; I

FIG. 5 is a crosssectional view of the plug in the extended positionshowing the expandable rubber ring in the relaxed position thusdiminishing the diameter of the rings, thereby allowing the plug to beplaced in the tube; and

FIG. 6 is a cross-sectional view of the plug positioned in the tubedownstream of the butted joint.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, theinternal orbital weld fixture 10, which per se forms no part ofapplicants invention, is clamped to a tube sheet 50 through aperture 11by weld clamp I2. The orbital electrode is aligned with and directedthrough aperture 15, the tip of the electrode 18 lying in a planeadjacent to a joint 48 between a tube to be mated and tube sheet. Leverarm 13 of weld heat acts as an alignment device to assure that theelectrode 18 is coaxial with the aperture 15. The sleeve 14 of welder 10is sealably engaged with aperture 15, thereby providing a gas-tightseal. A source of inert gas 16 is admitted through aperture and guidedtowards the vicinity of the electrodel8.

A plurality of tube sheet stubs 44 extend from a face 51 of tube sheet50. A plurality of tubes 46 are faced at the end to be mated to the tubesheet stubs 44 so that the tubes, when axially aligned with the stubs,are in total butt contact with one another. In order to assure alignmentof the tubes with the tube sheet stubs 44 and to perform other desiredfunctions, a chill bar generally designated as 20 is positioned over thetube and tube sheet stub. The chill bar 20 consists of a housing 22which in the horizontal position of the weld fixture and tubes is madeup of an upper housing segment 24 and a lower housing segment 26, thetwo segments being separable so that the clamp or chill bar may beplaced over the tube stub 44 and the butted end of tube 46. Screwfasteners 30 join the two segments 24 and 26 tofgether. An inert gasconduit 32 directs inert gas, such as argon, into an inner channel 34which directs the inert gas to a channel 36 defined around thecircumference of the segments 24 and 26. A circumferential cover plate37 closes off the channel, forming a manifold thereby. A plurality ofgas passages 38 are equidistantly spaced about the inner circumferenceof manifold 36 which direct argon gas radially inwardly through openings39 towards a groove 40. The groove 40, being on the inner periphery ofthe housing segments 24 and 26, forms a backup groove or casting die forthe molten weld puddle resultant from the welding operation. It has adepth of from 0.003 to 0.010 inch. The groove 40 encompasses the areawhere the end of the tube 46 mates with the face of the tube stub 44.The inlet orifices 39 communicating with gas passages 38 in segments 24and 26 do not line up in a plane adjacent the butted joint. The orifices39 are offset so that the molten weld puddle from the joint plane willnot be forced into the gas passages thereby preventing separation of thesegments 24 and 26 from the completed butt weld. The tip of theelectrode 18 from the orbital welder 10 lies on a plane adjacent thebutted joint 48 between the tubes 46 and tube stubs 44. The welder isaxially positioned so that the tip aligns perfectly with the buttedjoint.

Prior to inserting or installing the orbital welder 10 through orifice15, an internal gas plug generally designed as 60 is inserted throughorifice 15 with a special tool 90 and placed within tube 46 downstreamof the butted joint within the chill bar 20. A pair of expandable rubberrings 64 provides a gas-tight sealthus providing a plug for the incominginert gas that is fed through the orbital welder device 10 and directedto the vicinity of the welding operation, i.e., the butted joint. Ameasured orifice 74 in the end of plug 60 provides an escape route forthe gas impurities within the tube, for example, air, etc. The inert gasforces all of the impurities through the exhaust vent 74, thus providinga pure inert atmosphere for the welding operation. The size of orifice74 is between 0.006 inch and 0.010 inch thus the orifice is small enoughto maintain a higher pressure within the interior of this tube than thepressure that is maintained surrounding the butted joint. Similarexhaust orifices 42 are provided in the chill bar 20 to vent a portionof the argon supplied to the backup groove 40 through orifice 38 frommanifold 36. The plurality of vent lines 42 communicates between thebackup groove 40 and the exterior of the chill bar 20. By venting thebackup groove or chamber 40, it is assured that the weld puddle will beuniform within the groove 40. If the groove were not vented, there couldbe voids caused by trapped gas in the weld puddle being forced into thegroove.

in operation, argon gas entering through the orbital welder 10 beingsupplied to the vicinity of the welding operation is at a higherpressure within the interior of the tube than the pressure of the argonentering conduit 32 and directed towards the chamber 36. For example,the argon is within a pressure range of from 3 CFH to 12 CFH internally,while the argon in groove 40 is within a pressure range of l CFH to 10CFH. The higher pressure within and surrounding the tip of the electrode18 assures that as the welding operation proceeds, a molten weld puddleis forced into the backup groove 40 within chill bar 20, therebyassuring that the weld puddle will not fall out of the butted seam whilethe workpiece is in a substantially horizontal position. The increasedpressure interiorly of the welding operation forces the molten weldpuddle within the backup groove of casting die 40'.

Turning now to FIGS. 2 and 3, the housing 22 of chill bar 20 iscomprised of an upper housing segment 24 and a lower segment 26. Theupper segment 24 has extending from the segment a conduit 32. Theconduit 32 directs inert gas, such as argon, helium, etc., into aninternal conduit 34 which directs the inert gas into a channel 36, thechannel 36 is defined by an annular groove in both of segments 24 and26. The groove 36 is closed off by an external band 37 which forms themanifold. A plurality of conduits 38 directs argon from the manifold 36,out through orifices 39, the orifices being equidistantly spaced aroundthe circumference of the inner groove 40."The inner groove 40 providesan annular backup groove for the butted tube 46 and tube sheet stubs 44.The apertures 39, directing argon radially inwardly into the groove 40,are spaced at one end 41 of groove 40. Additionally, one or more exhaustports 42 communicate between the chamber or backup groove 40 andexterior of the chill bar 20. The outlet exhaust orifices 43 leading toports 42 are placed at the other end 45 of the groove or backup manifold40. Orifices 39 and 43 at opposite ends of groove 40 are spaced awayfrom the centrally positioned butted joint 5 i 48 to prevent the moltenmetal from being forced into the orifices 39, 43 by the increasedpressure of the inert gas within the interior of the tube and tube stub.The offset apertures 39 and 43, being spaced equidistantly around thegroove 40, will prevent the molten metal from flowing into theseapertures assuring that the two segments 24, 26 will separate uponcompletion of the welding cycle.

FIG. 3 illustrates how the segments 24, 26 are connected together bybolts in screws 30. A positioning L- shaped member 28 is clamped tosegment 24 of housing 22 by bolts 30. Shoulder 29 of positioning member28 rests on the face of an adjacent tube stub 44. The shoulder 29 servesto exactly position the chill bar 20 so that groove 40 within'chill bar20 exactly positions itself over the joint 48. Thus it can be seen thatthe chill bar 20 is accurately located each and every time it ispositioned over a mated tube and tube stub.

Turning now to FIG. 4, there is depicted a special tool generallydesignated as 90 that is used to install the tube plug 60 that ispositionable internally of tube 46 prior to the welding operation. Theinternal plug positioning tool 90 is comprised of a housing 92 which hasa rod 94 slidable within the tube 92. At one end 91 of the housing 92 isaffixed a pin 102. The pin 102 is engaged with the internal plug 60through a groove 78 within the outer housing 62 of plug 60. By insertingthe outer housing 62 into the groove 78 and twisting the tool 90 ninetydegrees relative to the internal plug, the tool is rotated through anarc of 90 opposite to the engaging motion and slipped out of the groove78. The rod 94 is slidable within the housing 92 within an axialdistance defined by groove 93. A pin 96, connected to rod 94, extendsinto the groove and acts as a stop for the axially sliding rod 94 withinhousing 92. A disc or shoulder 98 is provided at an end of the housing92 to provide a means to manually grasp the housing 92 relative to therod 94. A knob 100 is positioned at an end of the internal rod 94 sothat the rod may be pushed into or pulled out of housing 92.

FIG. 5 illustrates the internal plug 60 in cross-section. The internalplug 60 is comprised of outer housing 62 which defines the locking pingroove 78 for pin 102 of the insertion tool 90. Internally of thehousing 62 is an inner hollow cylindrical body 70 which slides withinthe outer housing 62. A shoulder 63 of outer housing 62 coacts with theshoulder 73 of inner cylindrical member 70 to define a chamber whichencloses an internal spring member 76. The spring 76 is biased to keepcylindrical body 70 retracted within outer housing 62. At the end of thecylindrical body 70 is a tip 68, the tip 68 is retained or connected tocylinder 70 by pin 72 (FIG. 6). Disposed between the tip 68 and thehousing 62 is a pair of resilient ring members 64. The ring member 64are separated by an annular ring 66. When the tool 90 is connected toouter housing 62, it can be seen that the end 104 of the internal rod 94is adjacent face 71 of internal cylinder 70. Since the outer housingmember 92 is engaged with housing 62 of the internal plug member 64 isless than the diameter of the internal plug housing member 62. Thus itcan be seen that when the internal rod 94 is forced against the internalplug member 70, the internal plug is extended in its overall axiallength, thus relieving the pressure on the resilient member 64 so thatthe internal plug can be easily inserted, in its extended position, withtube 64.

' Turning specifically to FIG. 6, the internal plug 60 is insertedwithin tube 46 in its extended condition by tool 90 and when the plug ispositioned accurately downstream of the butted joint 48, the pressure onknob 100 is released, allowing the spring 76 to retract the internalcylinder member 70, thereby compressing the rubber seal rings 64 adistance C so that the diameter then of the seal member 64 is greaterthan the diameter of the outer body 62, thereby locking the internalplug 60 within the tube 46. The diameter then of the seal member 64 isgreater than the inside diameter of the tube 46, thereby providing aseal for the argon gas being admitted to the interior of the tube. Oncethe pressure is released by tool 90, the tool can be rotated ninetydegrees to disengage pin 102 from housing 62,

and removed from the conduit 15 in tube sheet 50. The

welding fixture 10 is then clamped to the tube sheet for subsequentwelding of the butted joint 48, as previously described. An orifice 74is provided in tip 68 to vent a portion of the argon gas down theinterior of tube 46,

thus carrying with the vented argon any gas impurities remaining in theVicinity of the butted joint, such as oxidizing agents and the like.

We claim:

1. An apparatus to butt fusion weld a tube abutting a tube sheet stubmeans when said tube and tube sheet stub means are in a substantiallyhorizontal plane, comprising:

a chill bar means surrounding said abutting tube and tube sheet stubmeans, said chill bar means having separable segments;

manifold means defined by said segments, said manifold meanscommunicating with an inlet conduit in one of said segments;

weld puddle backup groove means defined by said segments of said chillbar means, said weld puddle backup groove means being adjacent saidabutting tube and tube sheet stub means;

one or more first inlet conduit means in said chill bar meanscommunicating with said weld puddle backup groove means and saidmanifold means;

' one or more second exhaust conduit means in said chill bar meanscommunicating between said weld puddle backup groove means and theatmosphere outside of said chill bar means,

orbital welding means positioned interiorly of said tube and tube sheetstub means positioned adjacent said abutted tube and tube sheet stubjoint to fuse said abutted tube and tube sheet stub means together,first inert gas means connected to said first inlet conduit meanswhereby inert gas from said first inert gas means enters said firstinlet conduit and is directed to said manifold means and passes intosaid first conduit means to said weld puddle backup groove means and outthrough said second exhaust conduit means to the atmosphere, therebyproviding an inert atmosphere for a molten weld puddle; and

a second inert gas means connected to the interior of said abutting tubeand tube sheet stub means whereby inert gas under pressure from saidsecond inert gas means enters the interior of said abutting tube andtube sheet stub means, the pressure of said inert gas from said secondinert gas means being at a pressure higher than the pressure of saidinert gas from said first inert gas means, thereby forcing the moltenweld puddle into said weld puddle backup groove in said chill bar means.

2. The invention as set forth in claim 1 wherein said I eating with saidweld puddle backup groove means and the atmosphere outside of said chillbar means is offset from said abuttment plane on the opposite side ofsaid weld puddle backup groove means from said one or more first inletconduit means so that the molten weld puddle is not forced into said oneor more second exhaust conduit means.

4. The invention as set forth in claim 1 further comprising a removableinternal plug means, said plug means sealingly engaged within theinterior of said tube means downstream of said chill bar meanssurrounding said abutting horizontally disposed tube and tube sheet stubmeans, said internal plug means serving to provide a seal for saidsecond inert gas means, the inert gas under pressure from said secondinert gas means being directed interiorly of said tube and tube sheetstub means, said inert gas under pressure from said second inert gasmeans serving to force said molten weld puddle into said weld puddlebackup groove means in said chill bar means 5. The invention set forthin claim 4 wherein said internal plug means comprises an inner and outerbody interfitted one with the other with a spring means interposedtherebetween, said spring means acting to retract the inner body withinsaid outer body, one or more resilient ring means positionedperipherally between radially extending shoulders on said inner andouter body, said one or more ring means, when said inner body isretracted within said outer body, being compressed so that thecircumference of said ring means is greater in diameter than the insidediameter of said tube means, thereby providing a seal between saidinternal plug means and the interior of said tube.

6. The invention as set forth in claim 4 wherein said plug means furtherdefines an exhaust port therethrough to pass a measured amount of inertgas through said plug means to carry out gas impurities existinginteriorly of said tube and tube sheet stub means.

7. An apparatus to butt fusion weld a tube abutting a tube sheet stubmeans when said tube and tube sheet stub means are in a substantiallyhorizontal plane, comprising:

a chill bar means surrounding said abutting tube and tube sheet stubmeans, said chill bar means having separable segments;

manifold means defined by said segments, said manifold meanscommunicating with an inlet conduit in one of said segments;

- weld puddle backup groove means defined by said segments of said chillbar means, said weld puddle backup groove means being adjacent saidabutting tube and tube sheet stub means;

one or more first inlet conduit means in said chill bar meanscommunicating with said weld puddle backup groove means and saidmanifold means;

one or more second exhaust conduit means in said chill bar meanscommunicating between said weld puddle backup groove means and theatmosphere outside of said chill bar means, and

orbital welding means positioned interiorly of said tube and tube sheetstub means, positioned adjacent said abutted tube and tube sheet stubmeans joint to fuse said abutted tube and tube sheet stub meanstogether,

an inert gas means connected to the interior of said tube and tube sheetstub means and to the interior of said weld puddle backup groove means,said inert gas means supplying inert gas under pressure, to said weldpuddle backup groove means adjacent said abutting tube and tube sheetstub means and to the interior of said abutting tube and tube sheet'stub means, inert gas flow splitting means serve to direct a portion ofsaid inert gas at a higher pressure in the interior of said abuttingtube and tube sheet stub means than the pressure in said backup groovemeans, the higher pressure in the interior of said tube and tube sheetstub means serving to force a molten weld puddle into said weld puddlebackup groove means in said chill bar means.

1. An apparatus to butt fusion weld a tube abutting a tube sheet stubmeans when said tube and tube sheet stub means are in a substantiallyhorizontal plane, comprising: a chill bar means surrounding saidabutting tube and tube sheet stub means, said chill bar meanS havingseparable segments; manifold means defined by said segments, saidmanifold means communicating with an inlet conduit in one of saidsegments; weld puddle backup groove means defined by said segments ofsaid chill bar means, said weld puddle backup groove means beingadjacent said abutting tube and tube sheet stub means; one or more firstinlet conduit means in said chill bar means communicating with said weldpuddle backup groove means and said manifold means; one or more secondexhaust conduit means in said chill bar means communicating between saidweld puddle backup groove means and the atmosphere outside of said chillbar means, orbital welding means positioned interiorly of said tube andtube sheet stub means positioned adjacent said abutted tube and tubesheet stub joint to fuse said abutted tube and tube sheet stub meanstogether, a first inert gas means connected to said first inlet conduitmeans whereby inert gas from said first inert gas means enters saidfirst inlet conduit and is directed to said manifold means and passesinto said first conduit means to said weld puddle backup groove meansand out through said second exhaust conduit means to the atmosphere,thereby providing an inert atmosphere for a molten weld puddle; and asecond inert gas means connected to the interior of said abutting tubeand tube sheet stub means whereby inert gas under pressure from saidsecond inert gas means enters the interior of said abutting tube andtube sheet stub means, the pressure of said inert gas from said secondinert gas means being at a pressure higher than the pressure of saidinert gas from said first inert gas means, thereby forcing the moltenweld puddle into said weld puddle backup groove in said chill bar means.2. The invention as set forth in claim 1 wherein said one or more firstinlet conduit means communicating with said weld puddle backup groovemeans is offset with respect to the plane of abuttment of said tube andtube stub means so that the molten weld puddle is not forced into saidone or more first inlet conduit means.
 3. The invention as set forth inclaim 2 wherein said one or more second exhaust conduit meanscommunicating with said weld puddle backup groove means and theatmosphere outside of said chill bar means is offset from said abuttmentplane on the opposite side of said weld puddle backup groove means fromsaid one or more first inlet conduit means so that the molten weldpuddle is not forced into said one or more second exhaust conduit means.4. The invention as set forth in claim 1 further comprising a removableinternal plug means, said plug means sealingly engaged within theinterior of said tube means downstream of said chill bar meanssurrounding said abutting horizontally disposed tube and tube sheet stubmeans, said internal plug means serving to provide a seal for saidsecond inert gas means, the inert gas under pressure from said secondinert gas means being directed interiorly of said tube and tube sheetstub means, said inert gas under pressure from said second inert gasmeans serving to force said molten weld puddle into said weld puddlebackup groove means in said chill bar means
 5. The invention set forthin claim 4 wherein said internal plug means comprises an inner and outerbody interfitted one with the other with a spring means interposedtherebetween, said spring means acting to retract the inner body withinsaid outer body, one or more resilient ring means positionedperipherally between radially extending shoulders on said inner andouter body, said one or more ring means, when said inner body isretracted within said outer body, being compressed so that thecircumference of said ring means is greater in diameter than the insidediameter of said tube means, thereby providing a seal between saidinternal plug means and the interior of said tube.
 6. The invention asset forth in claim 4 wherein said plug means further defines an exhaustport therethrough to pass a measured amount of inert gas through saidplug means to carry out gas impurities existing interiorly of said tubeand tube sheet stub means.
 7. An apparatus to butt fusion weld a tubeabutting a tube sheet stub means when said tube and tube sheet stubmeans are in a substantially horizontal plane, comprising: a chill barmeans surrounding said abutting tube and tube sheet stub means, saidchill bar means having separable segments; manifold means defined bysaid segments, said manifold means communicating with an inlet conduitin one of said segments; weld puddle backup groove means defined by saidsegments of said chill bar means, said weld puddle backup groove meansbeing adjacent said abutting tube and tube sheet stub means; one or morefirst inlet conduit means in said chill bar means communicating withsaid weld puddle backup groove means and said manifold means; one ormore second exhaust conduit means in said chill bar means communicatingbetween said weld puddle backup groove means and the atmosphere outsideof said chill bar means, and orbital welding means positioned interiorlyof said tube and tube sheet stub means, positioned adjacent said abuttedtube and tube sheet stub means joint to fuse said abutted tube and tubesheet stub means together, an inert gas means connected to the interiorof said tube and tube sheet stub means and to the interior of said weldpuddle backup groove means, said inert gas means supplying inert gasunder pressure, to said weld puddle backup groove means adjacent saidabutting tube and tube sheet stub means and to the interior of saidabutting tube and tube sheet stub means, inert gas flow splitting meansserve to direct a portion of said inert gas at a higher pressure in theinterior of said abutting tube and tube sheet stub means than thepressure in said backup groove means, the higher pressure in theinterior of said tube and tube sheet stub means serving to force amolten weld puddle into said weld puddle backup groove means in saidchill bar means.